This invention relates generally to bag filling machines for filling fine particulate powder into bags, and particularly to a dust-tight spout assembly having a vacuum discharge and a bag gripping assembly.
U.S. Pat. No. 4,526,214 to McGregor discloses a bag filling apparatus having a spout (2) incorporating two clam-jaw sections (4, 6) and an inner flexible tubular liner (122), and having a pair of dust collectors (88, 90) disposed on each side of the spout. Such an assembly is preferably utilized with the forming bars of the type shown in the bag hanging and gripping assembly disclosed in U.S. Pat. No. 4,322,932 to McGregor, although components of the bag gripping assembly are mounted on the spout as shown in the McGregor '214 patent.
In the McGregor '214 patent, the dust collectors are located in fluid flow communication with the interior of the suspended bag (140) adjacent the top end thereof, and are disposed overlying the open gap formed by the top of the bag between the gripping members (66, 68) and the side wall of the spout (4a, 4b).
Each of the dust collectors are characterized by generally rectangular ports (100, 102) along the bottom edges thereof, with interior bodies defined and enclosed by planar outer wall segments (92, 94) spaced apart from the side walls of the spout (4a, 4b) by spacer bars (96, 98). Each dust collector thus forms a generally flat enclosure with a port disposed above the top of the bag when the clam jaw spout is in the closed position, with the dust collectors pivoting in unison with the outer section (4) of the clam-jaw spout.
A pair of vacuum hoses (112, 114) connect each of the dust collectors to a source of negative pressure such as a vacuum pump (118). A separate vacuum line (136) is coupled to one of the vacuum hoses and connected to a passage (132) at the terminal end of the double-walled spout closure (30). The passage and spout closure extend along the entire length of the bottom edge of the clam-jam section of the spout, and the passage is located in fluid communication with the interior of the bag. Bag clamps (34, 36) hold the top edges of the bag in close contact with the bottom edge of each clam-jaw section of the spout, and are moved by double-acting power cylinders (58, 60).
The flexible tubular liner (122) is suspended within the spout and sealingly connected around the bottom opening of the hopper (1) to prevent airborne product from escaping the interior of the bag and the spout into the surrounding environment. The liner extends the height of the spout, with the bottom end of the liner received within the open top of the bag when the clam-jaw sections are open and the bag is being filled. The open bottom end of the liner is compressed together when the clam-jaw sections are closed and the bag is removed from the spout.
Each pair of gripping members (66, 68) are carried on arms (74, 76) that are pivotally mounted on opposing ends of a crossbar (75), and are pivoted inwardly toward one another and outwardly away from one another by a centrally mounted double-acting power cylinder (78) to simulate a pinching action to grip the top of the bag. Each crossbar (75) is connected to an upright member (77) which is carried on an overhead support structure that is pivotally connected to the hopper. Each set of arms on opposing sides of the spout is therefore moved laterally inwardly toward and outwardly away from the spout and dust collectors by a double-acting power cylinder that pivots the upright member (77), with the arms being moved inwardly toward the side walls of the spout as the clam-jaw sections of the spout are simultaneously opened. The extent of the lateral movement of the pair of arms is controlled by the predetermined range of movement of the double-acting power cylinder of the overhead support structure. This operation of the bag hanging and gripping mechanism is more fully depicted in the McGregor '932 patent.
While the dust-fight spout and bag handling apparatus disclosed in the McGregor '214 patent provides a suitable and workable alternative for many operations, there are some operational drawbacks presented by its structure.
The volume of air and particulate matter drawn through the dust collectors is limited by the area of the narrow rectangular ports, and the separate passage adjacent the closure is required to withdraw air from within the spout. This separate passage increases the number and size of the components disposed on the lower portion of the spout, thus affecting the capabilities of the bag hanging apparatus (and the accuracy and speed when hanging gussetted bags on a clam-jaw spout), and requiring additional vacuum line connections to that passage. The placement and movement of the bag handling assembly prevents increasing the dimensions of the dust collectors, and increasing the negative pressure of the vacuum pump can produce an unsuitable draw or flow velocity which unintentionally extracts product from within the bag as it falls from the spout or after it has settled within the bag. The number of double-acting power cylinders operating between predetermined ranges (particularly those controlling movement of the bag gripping arms) increases the complexity associated with programming the interrelated motions of the components when using an automated bag handling system. As the liner is compressed, creases and gaps may be formed between the confronting edges of the clam-jaw sections of the spout that permit product to spill from the spout and become airborne.